When transplanting the expression in 845d1b28bf57d3f1eb016a323cf15808c0fbfd85 I accidentally switched pants 1.3 to use the old pathspec, which breaks at runtime. This should fix it.
Pulling in the latest 1.3.0 release candidate from pants.
That means it'll build in Hydra and we don't really care which version of Python it builds against.